1. Field of the Invention
The invention relates to mixed media rendering.
2. Related Art
It is often desirable to send more than one type of media (known as “mixed media”) from a content server (or “originating server”) to a client device (or “terminal”) for presentation to a user. Mixed media can include: video, still images, vector graphics, bit maps, sounds, and other information for presentation to the user. MPEG-4 is one known method for encoding such mixed media scenes. MPEG-4 has a graph data structure, including the nodes of the graph, and links or relationships between pairs of those nodes. Information in this graph data structure describes the constituent elements of the scene to be presented.
One known problem with using MPEG-4 is that graphical display of different content and different media types (collectively known as objects) can raise significant performance issues. For example, when two objects or parts of objects occupy approximately the same spatial location in a MPEG-4 presentation, it may be unclear which object is to be displayed to a viewer. Similar problems exist when one of the objects is transparent or translucent (thus requiring that some portion of the both images must still be shown). An MPEG-4 display may include a large number of such objects, each requiring significant computation for correct presentation.
Another known problem is that the frame rate (that is, the number of frames that are displayed per second) is inversely proportional to the complexity of the graphical display. It is difficult to maintain a sufficiently fast frame rate when computing a complex stream without compromising the quality of the display.